The mouth is a complex biological ecosystem normally containing over 700 different species of bacteria. Some of these bacteria live in an exopolysacchride matrix biofilm and occupy specific niches in this complex oral environment. Understanding the oral environment and the microbiota that inhabit it will assist in determining their impact on health and disease. There are several studies in critically ill patients demonstrating changes in oral bacteria related to acute illness. Identification of respiratory pathogens in the mouth has led researchers to hypothesize that a relationship exists between the oral cavity and pulmonary infections. Identification of potential pathogens in the oral cavity of patients with severe aplastic anemia could indicate a similar association between oral pathogens and infection in patient who develop respiratory infections that are severe enough to require intubation. This descriptive case-control study will characterize the oral microbiota of patients who have severe aplastic anemia (SAA). Patients will be followed for 1 year after treatment for development of respiratory symptoms that require intubation (cases). The cases will be compared to two groups of controls, namely those SAA patients who did not require intubation that received treatment for SAA and normal healthy volunteers who are age and gender matched. A difference in the oral microbiome will be identified in specimens collected before and after treatment and in those patients who require intubation.